(a) Field of the Invention
The present invention relates to a method for determining a moving direction of a terminal and correcting a position thereof using a wireless local area network (WLAN), and a positioning apparatus using the same.
(b) Description of the Related Art
A positioning technology using wireless communication infrastructure is diverse according to a kind of infrastructure and a service range. A global navigation satellite system (GNSS) is a system which determines a position of a user using a signal of a satellite in an earth orbit, and a global positioning system (GPS) of America, a global navigation satellite system (GLONASS) of Russia, Galileo of Europe, and the like are being currently operated or are due to be operated. The GNSS is disposed to serve all over the globe, and is configured to include a satellite unit transmitting a signal including precise time information and satellite orbit information, a receiving unit receiving at least four satellite signals to calculate a position and a speed, and a terrestrial control unit monitoring and controlling a state and an orbit of the satellite.
The GNSS provides high position accuracy and availability within about 10 m in a plain or suburban districts in which a direct line of sight of the satellite unit and the receiving unit are secured; however, the GNSS has a problem in that a position error reaches 50 m due to a multipath error in a high density city area which is a non line of sight section, and particularly, received signal sensitivity deteriorates in the interior of a room to make it difficult to acquire a signal, such that a position and a speed may not be determined.
A cellular-based positioning technology is a technology of determining a position of a user using position information and a measurement signal of a mobile communication base station, and more specifically, is classified into cell-ID, enhanced-observed time difference (E-OTD), advanced-forward link trilateration (AFLT), and the like according to the number of base stations which may communicate with a terminal. Considering characteristics of mobile communication infrastructure having most of the downtown areas and the suburban districts as a service range, the cellular-based positioning technology may determine a position outdoors and indoors. However, the cellular-based positioning technology has different positioning accuracy depending on a disposition density of the base stations, and has relatively lower position accuracy of about 100 to 800 m on average and thus is hardly applied to interior and exterior navigation services and the like which require position accuracy of several meters.
An assisted GNSS (AGNSS) is a technology of acquiring ancillary information from a positioning server to improve the minimum received signal sensitivity of the GNSS receiver embedded in the terminal and shorten time to first fix. The AGNSS may quickly determine a position using the GNSS in the high density city area which is in weak signal environment, but may not obtain a large effect since the received signal is very weak in the interior area.
As a representative Wi-Fi-based positioning method for overcoming a difficulty in interior positioning as described above, there are a method for calculating a position of a terminal using a position and a measurement signal of a Wi-Fi access point (Wi-Fi AP), a fingerprinting method using a radio map of a Wi-Fi AP, and the like.
The Wi-Fi AP position-based positioning method estimates a collection position of a vehicle or a pedestrian and a position of the Wi-Fi AP using received signal intensities for each Wi-Fi AP, and calculates a position of a terminal based on positioning algorithms such as trilateration, weight centroid localization (WCL), Monte-Carlo, and the like, using the estimated position of the Wi-Fi AP. The fingerprinting-based positioning method processes the collection position of a vehicle and a pedestrian and the received signal intensities for each Wi-Fi AP to generate a wireless map of a reference position. Finally, the reference position having a minimum received signal intensity error is estimated as the position of the terminal by comparing Wi-Fi received signal intensity patterns for each AP which are measured by the wireless map and the terminal.
In connection with various positioning methods as described above, the Wi-Fi-based positioning technology may more precisely provide the position information of the terminal in the interior environment, as compared with the typical GNSS technology and the cellular-based positioning technology. However, the typical Wi-Fi-based positioning technology has a difficulty in calculating direction information (heading), which is other useful information, in addition to the position information.
In the typical Wi-Fi, the methods for calculating direction information are as follows.
First, when the position of the Wi-Fi AP is already known and the position of the terminal is calculated or when a fingerprinting DB including the direction and position of the terminal is already constructed even though the position of the Wi-Fi AP is unknown, the direction information between the AP and the terminal may be calculated using a beam antenna. However, since the method requires an expensive beam antenna and has considerable constraint conditions at the time of designing a terminal antenna, the method is inappropriate to apply to a commercial terminal.
Second, when the position of the Wi-Fi AP is known and the position of the terminal is calculated, the method may determine whether the terminal approaches or retreats from the AP using a change rate of the received signal intensity between the AP and the terminal. However, since noise of the received signal intensity is large in the general terminal environment, the direction of the terminal for the APs having a maximum cluster size is determined based on K-nearest neighbor clustering to remove an abnormal measurement value. The method may be applied to a commercial smart phone without an expensive beam antenna, but has reduced estimated direction accuracy due to instability of the Wi-Fi received signal intensity and therefore may not be applied to the fingerprinting method which does not know the position of the AP.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.